1. Field of the Invention
This invention relates to lubricating oil compositions and their use to minimize rust formation in internal combustion engines. More particularly, this invention relates to lubricating oil compositions which contain a supplemental rust inhibitor that is compatible with other components of such compositions and which are used in the crankcases of internal combustion engines to inhibit rust formation therein. In addition, this invention relates to a method for operating an internal combustion engine to inhibit rust formation, wherein a lubricating oil composition of the invention is employed in the crankcase of such engine.
2. Description of the Prior Art
A lubricating oil composition for an internal combustion engine contains various components in addition to a hydrocarbon oil of lubricating viscosity. Such other components furnish properties that are not present in the oil of lubricating viscosity but are needed to enable the composition to function properly and effectively in the crankcase of the internal combustion engine. One such component is that material which impedes or inhibits engine rust formation. An example is an overbased detergent, such as an overbased metal sulfonate or overbased metal phenate. The overbased detergent neutralizes the acidic components that are formed during fuel combustion. If a particular lubricating oil composition does not furnish sufficient protection against rust, additional overbased detergent can be added to the formulation. However, such tactics are limited by cost and performance restraints.
It is known that certain materials impede rust formation and should be capable of being used as supplemental rust inhibitors (SRI). Among these are ethylene oxide/propylene oxide block copolymers. However, these materials have the disadvantage of not being compatible with other typical additives in lubricating oil compositions. Consequently, their use as rust inhibitors in internal combustion engine lubricating oils is not practical.
These block copolymers, their derivatives, and related compounds, have been used to produce useful products. Such useful products are described in the art.
In U.S. Pat. No. 3,206,486, Nankee taught the preparation of long-chain unsaturated fatty acid monoesters of polyoxypropylene-polyoxyethylene block copolymer glycols and their use in brake fluids and similar hydraulic fluids and lubricants. He further taught that such brake fluids provide lubricity, non-corrosiveness, and compatibility with other commercial brake fluids.
In U.S. Pat. No. 4,493,776, Rhodes disclosed a supplemental rust inhibitor (SRI) additive comprising a combination of (A) R.sub.1 O[C.sub.2 H.sub.4 O].sub.x H and/or R.sub.2 O[C.sub.3 H.sub.6 O].sub.y H with (B) R.sub.3 O[C.sub.2 H.sub.4)].sub.x[C.sub.3 H.sub.6 O].sub.y H and/or R.sub.4 O[C.sub.3 H.sub.6)].sub.y [C.sub.2 H.sub.4 O].sub.x H, wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are hydrocarbyl radicals selected from alkyl, aryl, alkaryl, and arylalkyl groups or combinations thereof having from about 10 to about 24 carbon atoms and wherein x and y may vary independently in the range from 3 to about 15. He further taught that any lubricating oil composition having such SRI also should contain at least one overbased detergent additive as the primary rust inhibitor and at least one ashless dispersant.
In U.S. Pat. No. 3,235,502, Waldmann disclosed the product of the reaction of a fatty acid, such as oleic acid, with either ethylene oxide or propylene oxide, or mixtures thereof, in the presence of a basic catalyst, such as an alkali metal hydroxide, and its use as a foam inhibitor in oil compositions.
In U.S. Pat. No. 4,169,062, Weipert taught the product of a condensation reaction of an aliphatic fatty acid having from about 8 to about 22 carbon atoms in the chain with a mixture of ethylene oxide and propylene oxide in the presence of an alkali catalyst and the use of such a product as a synthetic fiber lubricant.
In U.S. Pat. No. 3,504,041, Weipert disclosed nonionic condensation products prepared by the condensation of an essentially linear primary aliphatic alcohol having from 10 to 18 carbon atoms in the aliphatic chain or a mixture of such alcohols with certain critical amounts of a mixture of ethylene oxide and propylene oxide and their use as surface active agents and as rinse additives in automatic dishwashing machines.
In U.S. Pat. No. 3,577,559, Horsley taught the product of a carboxylic group or phenolic group, a vicinal alkene oxide, such as ethylene oxide, propylene oxide, 1-butene oxide and 2-butene oxide, and a polymethylene cyclic ether, such as trimethylene oxide or tetrahydrofuran, to give a glycol ester or glycol ether containing the polymethylene cyclic ether moiety and the use of such product as a solvent, lubricant, hydraulic fluid, or chemical intermediate.
In U.S. Pat. No. 3,507,790, Beerbower, et al., disclosed oil-in-water emulsions suitable for use in glass molding and metal working operations, which emulsions contained the reaction product of ethylene oxide or propylene oxide with a compound selected from the group consisting of a partial ester of sorbitol, a fatty alcohol, a fatty acid, an aliphatic amine, an alkyl phenol, and mixtures thereof.
Now it has been found that a product prepared by reacting an ethylene oxide/propylene oxide block copolymer with a long-chain monocarboxylic acid and having a total acid number (TAN) that is in the range of about 10 to about 40 is a good SRI, which product is soluble and compatible with other components of a lubricating oil composition.